2. Solving for Legacy CO2: One Trillion Trees
All plants on Earth grow by harnessing sunlight, water and CO2 via photosynthesis. By pulling CO2 from the air around them, plants remove this greenhouse gas from the atmosphere, storing it in their roots and tissues. Thus, photosynthesis is a critical part of our planet’s carbon cycle, serving to maintain a balance in the greenhouse gas levels that influence our climate.
Photosynthesis is not the only natural process to sequester CO2, but it is the fastest. Over thousands or millions of years, geological processes can lock up CO2 in stable forms. On the other hand, photosynthesis begins capturing carbon as soon as a plant starts to grow.
Both types of processes have merit as we consider our options to stabilize Earth’s climate through carbon sequestration. However, the urgency of the climate crisis and our current emissions trajectory give added value to the fastest sequestration pathways. Slower drawdown methods mimicking geological storage may simply take too long to make an impact.
If we take decisive action towards broad scale sequestration, we will buy time to both transition to net-zero emissions and deploy long-term storage technologies like direct air capture or bioenergy carbon capture.
As the next three parts of this series will explore, there are a few different ways to utilize biological processes. Yet it is clear that planting trees is the most simple and direct way to utilize photosynthesis for carbon drawdown.
Reforestation in Japan. Credit: Carbon Brief
We know how to start, nurture, plant and care for trees. Additionally, they grow and live for decades or even centuries, holding and storing CO2 that whole time. Furthermore, trees offer a plethora of benefits, including:
Food, medicine, timber and other products.
Habitat for animals
Cleaning the air
Cooling local the climate
Erosion and flood control
Increasing regional rainfall
Recently, as more people become aware of our climate crisis, mass tree planting has gained notice as a potential solution too slow or even reverse global warming. A widely covered 2019 study by Thomas Crowther estimated that Earth could support 1.2 trillion new trees, which would offset 25% of legacy CO2 in the atmosphere.
Although this study was criticized for being overly optimistic, a more conservative estimate is that planting 1 trillion new trees could offset a decade of humanity’s annual CO2 emissions. Even this rate would be quite valuable.
Reforestation Project in China. Credit: Cosmos Magazine
Both the United Nations (UN) and World Economic Forum have campaigns aimed at the one trillion tree goal. But reaching this aspiration out in the real world and within a meaningful time frame will be quite challenging. Since 2006, the UN’s program counts 14 billion trees planted by corporations, nonprofits and individuals.
This means we need a paradigm shift in how we plant trees. We need new approaches that can scale up to plant a trillion trees within a decade. To make a dent in atmospheric CO2, we need to take bold action to start, nurture and plant trees on a massive scale across the globe.
Fortunately, innovative minds have already begun working on this very challenge. Multiple companies have built specialized drones for broad scale tree planting, particularly in remote and hard to access areas. For example, Dendra Systems, based out of the UK, claims it can plant trees 10x cheaper and 150x faster than people
These drones scan soil data and utilize mapping to determine the best planting locations, which they achieve by shooting seed pods down from above. Flash Forest, a Canadian company, claims they can plant 100,000 seed pods per day with drones operated by only two people.
Dendra Systems drone. Credit: Dendra Systems
Yet where, how and what we plant is critical. Simply shooting out millions of seeds from drones does not necessarily result in millions of trees.
Mass tree planting campaigns have mixed success. After all the work done to plant trees in a day, ongoing care gets neglected or the planting is done out of sync with the rains. Sometimes the species chosen aren’t well-adapted to the local climate or soils.
The social context is critical as well. Tree planting can disrupt the local community, or fail to account for why deforestation occurred originally, leading to trees being cut down once more. Monitoring can be forsaken after only a few years, failing to ensure that the trees grow to maturity.
For these reasons, it’s critical that tree planting is aware of both the local environment and community. We should choose adapted, resilient native tree species where possible, and know when to plant. Seedlings should be cared for in the initial phase after planting. Different species can be planted together, such as pairing a slow-growing overstory tree with a fast-growing, nitrogen fixing shrub.
Local communities must be involved, and have buy-in to the project, ideally through financial benefits tied to the newly-planted forest reaching maturity. In Grist’s examination of various large-scale tree planting projects, the work of a group in southern Brazil is highlighted as a success story.
There, native trees were planted that provided food and timber for the nearby community, ensuring their ongoing support and protection. Meanwhile, a corridor of forested habitat for the endangered black lion tamarin monkey was established and carbon was being sequestered by 2.7 million new trees.
One company that has thoroughly examined the need and associated challenges with planting one trillion trees is Terraformation. Started by former Reddit CEO Yishan Wong, Terraformation is applying principles from tech startups to the one trillion tree goal.
Wong’s team are solving bottlenecks like seed supply and nurseries, and tackling fundamental challenges like water supply by pairing seawater desalination with solar panels. With the ability to supply water from the ocean, significantly more land area could become viable for tree planting.
This would alleviate concerns about land use conflicts or trees displacing food crops, as the world aims to feed a billion or two more people this century.
Terraformation supplies companies, nonprofit organizations and governments with their streamlined nursery and seed bank kits, which can also operate off-grid. Beyond infrastructure, the innovative startup provides financing, software, training and help selling carbon credits for planted forests.
Tree planting is one of the cheapest and fastest methods to sequester CO2. However, once trees die, they do release much of the CO2 they were storing. New trees will grow in their place, and overall it is a net gain. Essentially, carbon cycles in and out of forests, rather than being permanently stored.
Trees are also vulnerable to climate extremes, whether from drought, fire, storms or pests, which could release their stored carbon. For example, the 2021 Bootleg fire in Oregon burned thousands of acres of timber meant to be preserved for carbon credits.
As they grow, trees steadily eat up carbon dioxide via photosynthesis, averaging 48 pounds of CO2 per year. Young trees appear to sequester more CO2 than old trees do, since they have less competition for light and therefore grow rapidly, whereas old forests slow their growth as they mature. Thus, the CO2 benefits are greater in the short term, which is still quite valuable.
One successful example we can be inspired by is China’s reforestation efforts in its southern regions over the past 15 years. NASA estimates that China, the world’s largest economy, has offset 20% of its annual fossil fuel emissions through large-scale tree planting.
If we could achieve a similar or greater offset of emissions on a global scale, we would allow more time to transition to a net zero CO2 emissions economy and deploy additional methods of CO2 capture.
Drones may turn out to be a viable way to rapidly plant trees. But as the world grapples with climate change and its impacts, there is something therapeutic about using our own two hands to make a difference.
Coordinated, worldwide tree planting days could unite us in taking one tangible action to slowly restore our climate. Whether in city streets, on strip mined hills or in the aftermath of a flood, planting a tree teaches us about regeneration and our ability to positively influence our environment.
